Field of the Invention
The present invention generally relates to apparatuses for automated nondestructive inspection (NDI) of metal structures, and, in particular, to apparatuses for automated nondestructive inspection of storage tanks for petroleum and petroleum products.
Prior Art
At present time different apparatuses for automated nondestructive inspection of metal structures are known, in particular, for inspection the bottoms of storage tanks for petroleum and petroleum products. Generally, apparatuses for nondestructive inspection based on the magnetic flux leakage method, which are used alone or in combination with apparatuses based on other non-destructive inspection methods are employed for nondestructive inspection. However all known apparatuses or systems for nondestructive inspection based on magnetic flux leakage method cannot provide inspection of various types of tank bottoms without direct human involvement, which often leads to the need for emptying and degassing of tanks.
For example, U.S. Pat. No. 5,514,956 discloses an apparatus for a storage tank bottom inspection based on a magnetic flux leakage method, which provides the possibility to decrease magnetic attraction of the apparatus device to the tank bottom in the presence of obstacles on the bottom surface by removing corresponding magnetic apparatus block from the surface of tank bottom. However, such decrease in magnetic attraction is to be provided by operator directly holding said apparatus and performing its movement, making it impossible to use said apparatus in the tank without emptying and degassing thereof. Furthermore, the use of other methods for nondestructive inspection in combination with the magnetic flux leakage method is not applicable in this apparatus, thus making the inspection by means of said apparatus less accurate.
Part of these disadvantages has been solved in the apparatus disclosed in U.S. Pat. No. 6,104,970, which is an automated apparatus for storage tank bottom inspection connected to remote station. Said apparatus can move along the surface of a tank bottom to be inspected, and comprises electromagnetic sensor and ultrasound sensors to enable nondestructive inspection of this bottom. Furthermore, the apparatus comprises a sensor to determine a butt or lap welded joint between the plates at the tank bottom, the signal from which enables removing of an electromagnetic sensor magnet to prevent a collision with the joint. However, in this case the inspection of tank bottom area at the location of joint and around it either is not performed, or a inspection accuracy of this area decreases significantly, thus decreasing greatly the overall inspection accuracy of entire bottom performed by means of said apparatus, especially in the presence of plurality of obstacles on the bottom to be inspected. Furthermore, the removing of the electromagnetic sensor magnet may not be a sufficient measure to allow for preventing collision with the butt or lap joint and magnetic attraction of magnet to the joint.
Thus, there is a vital need to provide an apparatus for nondestructive inspection, which can operate in the automatic or semi-automatic mode throughout the metal structure to be inspected comprising different obstacles and heterogeneities.